1 Introduction
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A distributed weighted fair channel selection and medium access control protocol, WF-MAC, has been developed for CCRN environment.
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Multilevel weighted fair resource utilization is maintained by the SUs through judicious channel selection and QoS-aware channel access.
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Efficient channel selection is performed through two-dimensional learning: channel availability prediction and channel utility perception.
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The results of performance study in ns-3 show significant improvements in throughput, weighted fair channel access, medium access delay, etc.
2 Related works
3 System model and assumptions
Type (Ω) | Description | Priority (ρ) |
---|---|---|
Voice | Highest priority (low latency) | |
(e.g., voice call, audio streaming) | 6 | |
Video | Second highest priority | |
(video conferencing, streaming) | 4 | |
Best effort | No QoS mentioned, bursty traffic | |
(traffic less sensitive to latency, e.g. | ||
web surfing) | 3 | |
Background | Lowest priority (no strict latency) | |
(e.g., print jobs, email, etc.) | 1 |
Notation | Description |
---|---|
\(\mathcal {M}\)
| Set of Licensed channels; { 1,2,3,…,m} |
\(\mathcal {N}_{r}\)
| Set of SUs of CRN r; { 1,2,3,…,n} |
Ω
| Set of traffic types |
ρ
| Priority value assigned to a specific traffic |
H
i
| Status of channel i; { 0,1,2} |
t
| Time needed to sense a channel |
σ
s
| Number of retransmissions for collision with SU |
σ
p
| Number of retransmissions for PU appearance |
\({\lambda ^{s}_{i}}\)
| SU arrival rate over channel i
|
\({\lambda ^{p}_{i}}\)
| PU arrival rate over channel i
|
\(\mathcal {E}\)
| Channel availability vector |
\(\mathcal {U}\)
| Channel utility perception vector |
\(\mathcal {O}\)
| Channel usage outcome { o
1,o
2,o
3,o
4} |
C
W
ρ
| Contention window for packet priority type ρ
|
4 Weighted-fair MAC design
4.1 Design components
4.2 Weighted fair channel selection
4.2.1 Channel availability prediction
4.2.2 Channel utility perception vector
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o 1 : SU has successfully transmitted a data packet.
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o 2 : SU transmission was deferred by collision withanother SU or bit error.
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o 3 : SU transmission was deferred by PU arrival.
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o 4 : SU has to switch from the current channel.
4.3 QoS-aware medium access
4.4 Channel switching mechanism
4.5 Discussion
5 Performance evaluation
5.1 Simulation environment
Parameter | Value |
---|---|
Deployment | |
Number of Channels | 10(data) +1(C
C
C) |
Number of CRNs | 7 |
Number of PUs | 10 |
Number of SUs per CRN | 15 |
Physical Layer Model | YansWifiPhy |
MAC Layer Model | ApWifiMac |
Transmission Range | 250 m |
Channel Data Rate | 7 Mbps |
Channel Bit Error Rate | 10−3
|
Packet Size | 1200 bytes |
Simulation Time | 1000 s |
Control | |
Propagation Delay, δ
| 0.83 μ
s
|
Size of RTS | 20 bytes |
Size of CTS, ACK | 14 bytes |
SIFS | 10 μ
s
|
DIFS | 50 μ
s
|
WF-MAC | |
Timeslot Duration, t
| 60 μ
s
|
\(\mathcal {T}_{switch}\)
| 120 μ
s
|
RCIV, CIV | 20, 260 bytes |
\(\epsilon_{th}^{s}\), \(\epsilon_{th}^{p}\)
| 0.4 |
ϕ
g
, ϕ
p
| 3 |
ϕ
s
| 10 |
γ
| 0.7 |
5.2 Performance metrics
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Throughput for SUs, \(\mathcal {P}^{th}\): Throughput is one of the major performance metrics used to evaluate the performance of any MAC protocols. It indicates the number of data bits that are delivered per second to the receivers. For our work, we are only concerned about the throughput performance of SUs, calculating the number of data bits they successfully transmit per second to their BSs.
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Average medium access delay, \(\mathcal {P}^{md}\): It is defined as the average time taken for a secondary user to get access of the medium before transmitting a packet, that is the time before SU could transmit the first bit of a packet. It is preferable to retain this access delay as minimum as possible.
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Protocol operation overhead, \(\mathcal {P}^{oh}\): It can be measured as the amount of control bytes exchanged per successful data byte transmission, i.e., we are measuring the portion of cost a MAC protocol pays for each byte of data transmission. It is always expected to lower this overhead for improving the performance of a protocol.
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Integrated performance improvement: The introduction of CIV and RCIV packets in the proposed WF-MAC forces to experience more protocol operation overhead compared to others. However, the integrated performance of WF-MAC is much better. We measure the integrated performance of the studied protocols as follows, \(\mathcal {P}^{\text {ip}} = \frac {\mathcal {P}^{\mathrm {{th}(bps)}}}{\mathcal {P}^{\text {md}}(s) \times \mathcal {P}^{\text {oh}}}\), which quantifies the cost compensation for the increased throughput and reduced medium access delay performances. We then calculate the performance improvement of WF-MAC by \(\frac {\mathcal {P}^{\text {ip}}_{\mathrm {WF-MAC}}}{\mathcal {P}^{\text {ip}}_{X}}\), where, X∈ {FMAC, nQ WF-MAC, random WF-MAC}.
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Channel selection percentage: We categorize the set of channels based on their availability into three quality levels, high, mid, and low. We measure the average percentage of selection from each category of channel over the total simulation period. A higher quality channel should have higher percentage of selection compared to a lower one.
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Medium access delay of traffic classes: It indicates the QoS awareness in medium access in our protocol. We calculate the average medium access delay of each type of traffic class over the active periods of the SUs. The average medium access delay experienced by a higher priority packet should be less than a lower priority packet.